508 HOWARD. [Vou. XIX. 
ments of the cone are at an angle of 45 degrees to the blue 
or yellow phase, in the upper field of the microscope, the 
half of the cone on the side of the yellow phase is blue and 
vice versa. By the theory that the reaction depends on the 
direction of the fibrils this would be accounted for by sup- 
posing that the cone was composed of fibrils whose direction 
was slightly ascending and oblique like the branches of a 
conical tree. In the yellow or blue position the fibrils on 
each side of the axis (or tree trunk) would not diverge 
enough from this axis to be at right angles to it and thus 
to give the same color to the whole, but between this posi- 
tion and that of parallelism with the axis there would be 
one where the color reactions would be opposite on the two 
sides of the axis. 
This difference between cones exposed and unexposed to 
light is possibly due to a difference in tension between the 
elongated and contracted conditions. If different sets of 
fibrils are present one may be tense while another is relaxed. 
However, since such fibers have *not as yet been seen and 
our knowledge of the outer segments of the cone is very 
limited, such considerations can be only speculative. 
D. EFFECTS OF REAGENTS. 
Early in this investigation I studied the effects of various 
fluids on the visual cells, particularly on the outer segments 
of rods, in order to obtain (1) neutral media in which 
intra-vitam stains could be used or other tests could be made; 
(2) suitable reagents for fixing and permanent preservation; 
and (3) means discovering the optical and other physical as 
well as chemical properties of these bodies. In judging of 
the state of preservation I compared the preserved material 
with living material in respect to its reactions to polarized 
light, its transparency, the form and behavior of its parts, 
and its subsequent staining, etc. 
The use of polarized light as a basis of comparison seemed 
eminently suitable, for, assuming that minute structural con- 
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